1. Field of the Invention
The present invention relates to a filtered cathodic arc source, wherein the filtering eliminates or reduces macro particles from the generated stream of plasma.
2. Background of the Invention
Cathodic arc deposition is an effective means for depositing thin films onto various substrates. A cathodic arc source apparatus generally includes a vacuum chamber, a cathode target having an evaporable surface which is made of the coating material, a means for igniting a stream of plasma at the cathode, and a substrate which receives the coating. If required, magnetic and electrostatic fields are generated to direct the plasma stream through the vacuum chamber and to the substrate.
A cathodic arc discharge occurs when a low voltage, high current power source is connected between the cathode and the vacuum chamber. Arc spots form on the surface of the cathode, producing a highly ionized stream of plasma which consists of vaporized cathode material including ions, neutral atoms, and electrons. The stream of plasma flows away from the surface of the cathode and is deposited on the substrate, forming a coating thereon. Cathodic arc deposition can also be used to produce a beam of high energy ions for ion implantation or surface modification.
A major benefit of cathodic arc deposition is the production of high density, uniform, adherent films. The films have excellent hardness and wear resistance, and can be deposited at very high growth rates. For example, diamond like carbon (DLC) coatings, which can be produced by using a graphite cathode, are exceptionally smooth and have diamond-like qualities, including extreme hardness, extremely low electrical conductivity, low coefficients of friction, and optical transparency over a wide range of wavelengths. DLC coatings are anti-corrosive and wear resistant, which make them particularly desirable for semi-conductor and tool manufacturing applications.
A problem associated with cathodic arc deposition is the generation of macro particles in the form of droplets of molten target material of about 0.1 to 50 microns in diameter. Macro particles are produced at the arc spot when the presence of the arc superheats the cathode target. Macro particles cause surface irregularities in the deposited coating by becoming either permanently imbedded or temporarily affixed in the coating and later detaching. Macro particles thus result in undesirable non-uniformities which make the coatings unsuitable for particular mechanical, electronic, and optical applications.
Two solutions to the above cited problem have been developed in the prior art. The first prevents macro particles from forming by controlling the location of the arc on the surface of the cathode target, and the second filters macro particles from the plasma stream before they reach the substrate.
Conventional methods of controlling the arc path over the surface of the cathode target include steering the arc by using magnetic fields and/or employing a cathode target of a particular shape. For example, U.S. Pat. No. 5,480,527 to Welty discloses a rectangular planar cathode and a magnetic field reversal technique which eliminates the splattering of molten droplets which form macro particles. Welty teaches reversing the magnetic field each time the arc reaches one end of the rectangular cathode, causing the arc to scan back and forth along the cathode surface and preventing any one region of the cathode from getting hot enough to "splatter" particles.
U.S. Pat. No. 5,126,031 to Tamagaki, et al. discloses generating a magnetic field that causes the arc spot to rotate circularly and at a high velocity. This design also reduces the generation of macro particles by shortening the time the arc spot resides at a certain position on the cathode target.
Although arc steering methods represent simpler solutions than filtering methods, arc steering does not completely eliminate macro particle generation. In addition, where a magnetic field is also used to separate macro particles from a plasma stream, the macro particle separation magnetic field may be stronger than and interfere with the arc steering magnetic field, such that control over the arc position is lost.
Conventional filtering methods provide for an angled vacuum chamber or plasma duct configuration, where no line of sight exists between the cathode target and the substrate. Using this technique, a magnetic and/or electrostatic field guides the plasma stream through the angled plasma duct and to the substrate. While the plasma stream bends around the elbow of the duct, macro particles, which are unaffected by the magnetic and/or electrostatic field, continue along the initial trajectory, substantially a straight line, and are thus separated or filtered from the plasma stream. In addition, baffles or traps can be used in an attempt to prevent macro particles from being deflected in the direction of the substrate by angled or curved plasma duct walls.
U.S. Pat. No. 5,279,723 to Falabella, et al., discloses a bent plasma duct in which two straight solenoids placed end-to-end and at a 45 degree angle generate a magnetic field with magnetic field lines nearly parallel to the bent plasma duct walls. The magnetic field constrains the electrons in the plasma stream, and the flow of the electrons produces the electrostatic field required to guide the ions around the bend in the plasma duct. In addition, a series of baffles comprised of annular rings are provided along the duct walls to trap and deflect macro particles away from the substrate.
U.S. Pat. No. 5,433,836 to Martin, et al., discloses filtering macro particles by using a minimally non-linear duct, in addition to an extended magnetic field which produces the required bending and confining of the plasma. The extended magnetic field is generated by toroids to define the non-linear plasma duct, which comprises a tubular anode having a length that is six times greater than the length of the cathode.
Although filtering systems may successfully remove larger macro particles from the plasma stream, not all macro particles are effectively filtered. Furthermore, the use of an angled or curved plasma duct dictates that macro particles which strike the duct wall are likely to bounce or be deflected in the direction of the substrate, despite the use of baffles.
There exists a significant and continuing demand for filtered cathodic arc sources which eliminate macro particles from the deposited coating.
Therefore, in view of the above, a basic object of the present invention is to separate macro particles from a stream of plasma generated by a cathodic arc source, such that macro particles are not present in the resultant coating.
Another object of this invention is to use a transverse magnetic field to guide a stream of plasma to a substrate, wherein the substrate is not in the line of sight of the cathode target.
Another object of this invention is to position a particle deflector within a vacuum chamber of a cathodic arc source which intercepts and deflects macro particles away from the substrate.
Yet another object of this invention is to provide a macro particle deflector having a conical and tapered surface, including a flange, for deflecting macro particles away from the substrate.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of instrumentation and combinations particularly pointed out in the appended claims.